Tachometer generator with suppressed spurious quadrature voltage effects



3,252,026 ous J. E. FOSTER RATOR May 17, 1966 TACHOMETER GENE WITHSUPPRESSED SPURI VOLTAGE EFFECTS une 28, 1965 QUADRATURE Filed J UnitedStates vPatent O 3,252,026 TACHOMETER GEN ERATGR WITH SUPPRESSEDSPURIOUS QUADRATURE VOLTAGE EFFECTS Julius E. Foster, 2431 Webb Ave.,Bronx, NSY. Filed June 28, 1963, Ser. No. 296,416 17 Claims. (Cl.Sith-171) This invention relates to tachometer or rate generators,inwhich the usual spurious quadrature voltage effects, caused byharmonic fiux components of the flux field, are suppressed, thereby toeliminate the usual quadrature null or zero error voltage.

This application isa continuation-impart of my copending -applicationSerial No. 783,738 filed December 30, 1958, allowed November 2, 1962,now abandoned.

Tachometer generators are dynamo-electric devices for generating anelectromotive force in a stationary stator winding, that bears a directlinear relationship to the angular velocity of the rotor part of thegenerator.

The tach generator construction usually includes a primary or inputstationary winding distributed in radial slots of a primary cylindricalstator core that is concentric with the axis of rotation. A secondarycore is concentrically disposed around the primary core and supports asecondary or output distributed stationary winding. The secondarywinding is angularly spaced with respect to the primary winding by anangle of 90 electrical degrees, so that the secondary winding is in`quadrature electrical spacing from the primary winding, and is intendednot to be energized from the 'primary winding during stationaryconditions of the generator.

The two stator cores are separated by a narrow cylindrical air gap,within which a rotor, in theform of a cup, is driven by an associatedmotor or other device at the speed which is to be measured. The rotorcup serves as the energy coupling or transfer element between the twowindings, and its rotation determines the voltage generated in theoutput winding of the tach generator.

In another construction, both windings are disposed on one inner core,also in electrical quadrature spacing, within the inner diametricallimits of the rotor cup. A stationary outer core, encircling the cup,serves to provide the magnetic return path for the flux from the innercore, and such outer core defines the outer limit of the air gap aroundtheinner core. The main flux field from the primary winding crosses thisair gap through the wall of the rotor cup.

The tach generator is essentially a transformer with two stationarywindings in electrical quadrature relation, whose electro-magneticcoupling is controlled by the rotatable cup. The cup is of non-magneticmaterial. When the cup is at rest, it does not serve to couple thewindings, and does not transfer any energy between them. However, whenthe cup rotates, it transfers energy from the primary winding to the`secondary winding.

In an ideal tach generator, no voltage or electro-motive force would beinduced in the secondary winding while the rotor cup is at rest. Theoriginal disposition of the secondary winding in electrical quadratureposition relative to the primary winding, is intended to assure that noelectromotive force will be generated in the secondary winding, from theprimary winding when the generator rotor is at rest and the cup is notmoving between the two windings. However, in conventional tachometergenerators, because of the dificulty of -actually controlling thedisposition of the paths of travel of the entire electro-magnetic fluxfield from a winding, some components of the fiux field from the primarywinding induce an undesired spurious electromotive force in thesecondary winding, even while the rotor cup is at rest.

These spurious voltages are, to a great extent, due to frequency butalso to the harmonic components of the magnetic flux field of theprimary winding. Such harmonic components of the flux field result fromthe nature of the winding distribution.

In the tachometry generator here contemplated, the energy isltransferred through the medium of an alternating electro-magnetic fluxfield. To achieve .the -optimum desired relationship between lsuch aflux field and its effect, the fiux field should be sinusoidal. However,because such a flux field must necessarily be established by windings orcoils that are not continuous in -their disposition and effect, the fluxfield portions or components are individually mathematicallydiscontinuous or sudden, in steps, and are generally characterized asbeing of rectangular or square wave shape.

A step or square wave as a mathematical function is mathematicallydefined by a Fourier series expansion consisting of a sinusoidalfundamental frequency term and a series of harmonic terms that representmultiple frequency sinusoidal components, all of which when addedtogether synthesize or form the square wave as the total or sum of theentire Fourier series.

In dynamo-electric apparatus, the windings, or coils constituting thewindings, are laid in slots in a core of `magnetizable material such asiron or steel. Electrical currents traversing the windings, or coilsides, in passage, develop magneto-motive forces and consequent magneticfiux fields to magnetize the core. The usual distribution of thewinding, or of the coil sides, in the associated supporting core, issuch as to for-m a magnetic flux field that must take a square wave formin its values.

Consequently, the square wave flux field contains, and must unavoidablycontain, harmonic components corresponding to the sever-al harmonicterms of the Fourier series that defines a wave of that shape. Moreover,those harmonic components must exist in the same ratio or amplituderelationship as defined by the corresponding term-s of that Fourierseries.

Thus, an energizing current when supplied tothe winding must supply notonly energy to develop the flux field component for the fundamentalfrequency that is to accomplish the desired work, but must also supplyenergy to develop the several flux field components of the severalharmonic frequencies corresponding to the Fourier series terms, eventhough they are not wanted. Consequently, the energizing current mustinclude magnetizing current component-s to magnetize the core body withmagnetic fluxes corresponding not only to the wanted fundamental uwantedharmonic frequencies.

The unwanted harmonic frequency components of magnetizing current `andof the consequent flux field are detrimental. But, because of theunavoidable type of winding and coil distribution and the consequentform of flux field formation, those undesired harmonic components arepresent and they cause the existence of detrimental other effects.

In the core -supporting the primary winding, the harmonic fluxcomponents saturate the tooth edges and core along the -slot containingthe coil sides. Consequently, the core body area is reduced that is tobe available to the main or fundamental fiux component, and moremagnetizing current is needed.

One of the most troublesome errors in a tachometer generator in aspurious quadrature voltage. The proper operation of the tachometergenerator depends upon the production of a true quadrature voltage inthe secondary winding by the energy-transferring operation of therotating cup. The spurious quadrature voltage is caused by thefrequency-.modulation effects resulting from intermodulation of thevarious harmonic flux components, and therefore the spurious quadraturevoltage is present in the output, even while the cup is at rest, andthen throughout the full range of speed of the rotor cup.

Moreover, during operation of the cup, the flux field of and oftroublesome errors that prevent the induction of a linear output voltagethat is a direct function of the cup speed. Present conventional methodsfor eliminating spurious quadrature voltages require individual testingof each tachometer generator to determine its idiosyncrasies, and thenapply a cure to the symptoms rather than to the cause.

The present invention is directed to a new philosophy shown embodied ina construction and directed to ay method of operation in electricalapparatus that will substantially reduce the ma'gnetizing current neededfor the harmonic flux components and that will isolate those harmonicflux components and separate them from the regular magnetic circuit pathdesired for the fundamental flux field. As a consequence, the fullbenefit of the fundamental flux field energy is obtained withoutinterference from spurious voltage effects other-wise caused by theharmonic flux components.

The primary object of this invention therefore is to provide a noveltach generator in which the ideal linearity characteristics may be moreclosely achieved.

A further object of this invention is to provide a novel principle ofconstruction and design for a tachometer generator whereby the harmfuland spurious effects of various types of electrical harmonics may besubstantially suppressed and eliminated, or the harmonic flux componentsdiverted to a path or region where they will have no harmful effect onthe intended or desired operation of the apparatus.

Another object of the invention is to keep the harmonic fiux componentsout of the air gap and to prevent them from interlinking with certainpredetermined operating windings thatwould otherwise be interlinked.v

Another object of the invention is to keep the harmonic fiux componentsout of the core body for the operating windings.

Another object of the invention is to provide a tach generatorconstruction in which only the fundamental fiux component is permittedto cross the air gap, and all other iiux components are confined to arestricted and ineffective path to prevent possible harmful interlinkagewith the operating windings.

These objects are generally achieved by establishing an auxiliarymagnetic path for the harmonic flux components and by th-us divertingthe harmonic fiux components from the main path intended for the mainoperating flux field.

For maximum benefit, the harmonics should be kept out of the corestructure and also should be kept out of an air gap, where the operatingfiux path includes such air gap. In some cases, the partial benefitsderived from keeping the harmonics out of the core alone or out of theair gap alone may be sufficient.

v Thus, different modifications may be employed, to utilize theinvention in full or in part.

These objects are achieved in one modification by wrapping all the coilsides of each coil in a strip or sheet of softly magnetizable foilhaving a thickness of about 0.001 inch, with one or more layers asneeded to provide a closed magnetic circuit that will saturate by theharmonic iiux content of the magnetic fiuX field from the primarywinding. In order to achieve the full benefit of this invention, theentire coil including coil sides in the slot and coil end turns areenwrapped in the magnetic foil.

In dynamo-electric devices with small coil slots, some inconvenience isexperienced in the placement and handling of suchl thin foil.

To avoid this difficulty, a further feature of this invention is toutilize the insulating material which will usually be used for the coilslots, and to use that insulating material as a carrier for supportingand handling and placing the magnetizable material that is to providethe auxiliary magnetic path for the harmonic iiux components. Suchinsulating material may be treated to embody a layer of magnetiZa-blematerial to serve the function of the thin foil. Thus, the insulatingmaterial which is easily handled in its conventional way, fordisposition in the slots, also serves the additional purpose andfunction of supporting and locating or positioning the body ofmagnetizable material in appropriate position to enable thatmagnetizable material to serve as an auxiliary magnetic path for theharmonic fiux field components, and to vdivert those harmonic componentsand to confine them to a path where they will be ineffective to causeharmful effects.

The insulating material is frequently in the form of a roll of plasticfilm or tape, a commercial example of which is the tape made by du Pontand sold under the trade-mark MYLAR. This tape may be treated to cementthereto finely divided magnetic particles of relatively highpermeability and low magnetic retentivity, commercially available invarious forms as magnetic iron, iron alloys, or ferrites. Thisconstruction permits the tape, which is easily handled, to serve as acarrier for the magnetizable material, and permits the placement of themagnetizable material `to be easily accomplished While placing the tapein the usual conventional procedure.

The magnetiZa-ble material may take any form which will present across-sectional area that will be substantially saturated by theharmonic flux components of the magnetic field that will `be developedby the related coils or coil sides. Thus the magnetic material may beone or more layers of thin magnetizable foil, continuous or in spacedstrips, or a layer of finely divided particles, or a woven fabric ofmagnetizable threads, or any other structural form that will present asaturable cross-sectional area to the unwanted harmonic fiux components.

For high-temperature operation, the insulating base material may be astrip or layer of asbestos, or equivalent material, with themagnetizable material consisting of magnetic filaments or fabricsupported on or in the asbestos layer or strip, or consisting of one ormore imprints of magnetic ink on the insulating base material.Similarly, the magnetic particles or foil may be attached or lbonded tothe base insulating material by any suitable cement or bonding agentthat will tolerate the operating temperatures.

This `form of insulating material combined with the harmonic uxdiverting magnetizable material is described and claimed in Imyco-pending application Serial No. 51,696, filed lune 25, 1963. As theredescribed, the combination of insulation and magnetic material is ofutility in various forms and applications in electromagnetic devices andin dynamo-electric apparatus.

Thus, the insulation directly applicable to slots and windings mayinclude a tape type of insulation for Wrapping a winding or for lining aslot. In dynamo electric machines of larger capacity, the slot linersmay be self-supporting fiberboard liners between windings and core orbetween windings of separate phase in one slot. In such applications,the harmonic uxes are kept from affecting the core and tooth edges thatIborder a slot, and and also serve to prevent inductive iiuxinterlinkage between the separate winding that may occupy the same slotin common.

In the construction of the tachometer in which the windings are onopposite sides of the air gap, slot wedges may be employed to preventharmonic iiuxes from entering or crossing the gap which would otherwisecause undesired harmonic inductive effects between the windings bytransfer into and through the rotatable cup.

The objects of the invention are thus similarly achieved in bothmodifications, in which the tape or other insulating material may bedisposed in usual manner to line a slot to provide insulation betweenthe lamination edges at the slot and the wires or conductors to beplaced in the slot, or the slot wedges with magnetizable material may beemployed to close the slots and thereby prevent harmonic fiux movementinto and -across the air gap.

The manner in which the invention is applied is illustrated inconnection with a tachometer generator having two spaced cores, as shownin the accompanying drawings, in which FIGURE l is a perspective view ofa tachometer generator, with the rotatable non-magnetic induction rotorcup shown axially withdrawn from its normal position in the air gapbetween two concentric cores forthe respective windings;

FIGURE 2 shows the windings of the motor and tachometer generatorschematically;

FIGURE 3 is a schematic development of opposite portions of the twocores and shows the relative disposition of the two windings, and theirend turns, and the approximate disposition of the paths and theturbulent effects of the harmonic fiuxes;

FIGURE 3-A is a View similar to FIGURE 3 showing the absence of magneticturbulence effects in the core and teeth after the application ofsaturable magnetic foil around the coil sides in accordance with theinvention;

FIGURE 4 is a schematic sectional View ofen-d portions of the two coresand the rotor cup and the end turns of two opposite coils, to indicate atypical path and arrangement of leakage fluxes between the end turns ofopposite adjacent coils of the two windings, as a result of themagneto-motive forces setup in the end face sufaces of the teeth of theouter laminations;

FIGURE 5 is a graph showing the square wave or step form of the magneticfiux field generated by the primary winding coils when energized;

FIGUR-E 6 is a graph showing the first three terms of a Fourier `seriesexpansion mathematically defining' the rectangular step wave in thefigure;

FIGURE 7 is a graph showing the trapezoidal form of the rfiux fieldunder conditions of the load, or output in the secondary winding, andshows the spike impulse at the end of the flux field form;

FIGURE 8 is a graph showin-g the equivalent spike termination on thetrapezoidal flux wave of FIGURE 7 as a unit impulse;

FIGURE 9 is a schematic sectional view of a pair of slots, to show howthe magnetic foil is disposed around the coil sides to provide aconfining path for the harmonic flux components; and

FIGURE l0 is a schematic view of a tachometer generator in which bothwindings are on the same core structure.

As shown in FIGURES l and 2 of the drawings, a conventional tachgenerator 20, of a type modified according to this invention, comprisesa primary core 21 and a secondary core l22 spaced fromthe primary coreto define an air gap 23 in which a rotor cup 24 is rotate-d by a motor25.

The primary core 21 supports a primary winding 26 and the secondary coresupports a secondary winding 27. As indicated in FIGURE 2, the secondarywinding 27 is disposed to be in electrical quadrature relative to theprimary winding 26. -It is desired that no electromotive force shall beinduce-d in the secondary winding 27 from the primary winding 26 whenthe cup 24 is stationary. However, when the cup is rotated in the airgap 23, it is to be effective to transfer energy inductively from theprimary winding 26 to the secondary winding 27.

Each of the two windings 26 and 27 consists of several coils in series,which are disposed on their respective cores in the manner shown inFIGURE 3, showing a development of the core and winding arrangement. Therelative direction of coil turns is well known.

In' such `conventional tachometer generator, in the absence of thepresent invention, the harmonic flux components of the magnetic fluxfield generated by the primary winding -26, as in FIGURE 3, willestablish a saturated condition along the slot edge surfaces of theteeth, as at 30, on the laminations of tooth 31, for example, and alongthe slot core body, as at 32, adjacent the coil sides 3'3, as in slot34, for example, in FIGURE 3. To illustrate this condition, part of theouter end lamination 35 is broken away, in FIGURE 3, to expose the nextlower lamination 36, both in tooth 31 of core 21, and related as shownmore clearly in FIGURE 4. This saturated condition in slot tooth edgeand in slot core body edge is established by the coil slides 32 in theslots.

The end turns 37 of the coils similarly affect the outer or endlamination 35. The outer surface 38 of that outer endilamination 35becomes magnetically saturated, as indicated in FIGURES 3 and 4. Themagneto-motive force established by the end turns 37 supports theharmonic yflux components to similarly saturate the outer surface 39 ofthe outer end lamination 41 of the aligned tooth 42 in the upper orsecondary core 22. The leakage flux between the two cores is generallyindicated by liux lines 43.

The depth of saturation is a function of the thickness of the laminationand of the amplitudes of the harmonic fiux components as related to therelative amplitude of the corresponding term of the pertinent Fourierseries that defines the flux wave form function. Thus, the content andvalues of harmonic flux components may vary under load, according to thechange in shape of the ux field wave form.

For example, as previously indicated, a slot and tooth structure `withdistributed coils, as in FIGURE 3, will generate a step wave flux field,of the form 45 in FIG- URE 5, which contains a series of harmoniccomponents as defined by the corresponding Fourier series expansion forthe mathematical function represented by a graph of the same shape asthe fiux field. In FIGURE 6 the first three flux wave components 46, 47and 48, only are shown, corresponding to the first three terms of theFourier series expansion, representing the fundamental, the thirdharmonic and the fifth harmonic. The further terms are not shown,although necessarily present.

The square or step wave 45 of FIGURE 5 represents the fiux wave atno-load, while the rotor cup is at standstill. When .the rotor cupbegins to rotate and attains a substantial speed, the generator 20becomes loaded, and the fiux field wave form changes to the trapezoidalform 50 shown in FIGURE 7. When the harmonics combine to form thistrapezoidal form of flux wave 50, the effect is equivalent to asuper-position of a ramp function 51 on a step 52 of reduced amplitude.The added feature,

of importance here, is the formation of the spike 55 at the end of theramp function 51. (See Goldman: Frequency Analysis, Modulation andNoise, 1948, McGraw Hill, pages 30-32.)

The spike 55, in its action, is essentially a unit impulse shown at 60in FIGURE 8. The unit impulse has a special effect between the adjacentend turns of the opposite primary and secondary windings. The impulse isof sufiiciently high frequency to enable and to cause the end turns ofthe primary winding to act as short radiating dipole antennas.

The end turns 37 of the primary winding thus transmit energy in twoundesirable forms to the secondary winding. First, the leakage inductionis transmitted in the manner shown in FIGURE 4. In terms of antennatheory, this leakage fiux may be considered to be nearfield effect. Herethe air path dimensions are significant and limit the leakage flux.Second, the spike and impulse effects establish the far field effects.Then the air path or space between the end turns of adjacent coils ofopposite windings is not material, since the energy pulses are radiated.

Thus in conventional constructions of tachometer generators, spurious orleakage energy is transmitted from the primary winding to the secondarywinding through the core 4by magneto-motive force action and consequentleakage through the iron, and also by similar end-turn leakage andradiation. Such spurious and leakage energy manifests itself in falsebut substantial so-called zero error or null voltage in the secondarywinding, although the rotor cup 24 is actually at standstill, and novoltage should be in the secondary Winding.

In the absence of any such spurious induction effects between theprimary winding 26 and the secondary winding 2'7, the rotor cup 23 wouldaccurately induce in the Secondary winding 27 an electro-motive forcethat is substantially a direct linear measure of the angular speed f thecup 23. vWhen the rotor cup 23 is rotated, it induces into the secondarywinding 27 a voltage in electrical quadrature with the voltage acrossthe primary winding 26.

However, independently of the energ -transfer effect of the rotor cup23, which acts solely during rotation, the intermodulation of theharmonic ux components of the electro-magnetic eld from the coils of thestationary primary winding 21 establishes a quadrature harmoniccomponent which reaches and energizes stationary secondary Winding 27.(See Goldman, cited above, pages 167 et seq.) The energy for suchquadrature component is drained from the fundamental by suchintermodulation action. Thus, a spurious electrical quadratureelectromotive force is induced in secondary winding 27, that is in noway due to the rotation of the rotor cup Z3. Such spurious electricalquadrature electro-motive force exists in the secondary winding 2'7under all operating conditions, whether the cup is stationary or isrotating.

As a result, both the desired real quadrature voltage, induced by thecup, and the undesired spurious quadrature voltage caused by harmonicintermodulation are present in the secondary winding. The realquadrature Voltages and the spurious quadrature voltages arealgebraically additive, and are ditlicult to separate when oncecombined.

However, by the principles of this invention, the undesirable spuriousquadrature induction effect is prevented from combining with the truequadrature voltage, and is kept out of the secondary winding 27, so onlythe true quadrature voltage is present in the secondary winding 27.

The intermodulationbetween the harmonic flux components and thefundamental tlux component is prevented by conning the harmonic lluxcomponents to a limited 8 of 0.001 inch or less. The total cross-sectionof the wrapping of foil, in one or more layers, is such as to besaturable by the harmonic flux components. Under such conditions, thefoil presents a path of low permeability to the fundamental flux, whichthen seeks its path of high permeability as if the foil were not there.

In the absence of the foil '70, the harmonic uxes magnetize the slotwall surfaces, representing a partial depth into the teeth, as shown inFIGURES 3 and 4. Consequently, the effective tooth width is reduced andthe flux density of the fundamental flux component increased.Consequently, the necessary magnetizing current is increased for thefundamental flux component, with a correspondingincrease in magnetizingcurrent for the harmonics themselves, since the Fourier ratios alwayshave to be maintained.

The foil 7t), however, when disposed in the slot, between coil turns andteeth or core, absorbs the harmonic fluxes and connes them to the pathin the foil. The beneficial results are reduction in magnetizing currentand increased efliciency, but mainly prevention of intermodulation andprevention of leakage and transfer of' spurious energy to develop aspurious quadrature voltage in the secondary winding. This feature ofeliminating the false quadrature voltage is of prime importance sincethe tachometer generator is to serve as a measuring instrument of highaccuracy.

Thus, by this invention the foil serves to separate the spuriouselectrically initiated quadrature voltage from the real quadraturevoltage mechanically vinitiated by the rotating rotor cup 23. By thissingle expedient, the foil also keeps the spurious quadrature voltageout of the secondary winding and eliminates the spurious zero error ornull voltage heretofore compromisingly accepted as a necessary evil inthe operation -of a tachometer generator.

Referring back now to FIGURE 3A, the same structure as of FIGURE 3 isshown, but with the coils enwrapped and protected by a magneticallyclosed wrapping of one or more layers of m'agnetizable thin foil '70.For the present application, where maximum accuracy is sought, the coilturns of the entire coil are preferably encircled by the foil Wrappingin one or more layers at different parts of the coil, as, for example,on the coil sides in the slots, and on the end turns beyond the lamina-I tions. The llux density and the total flux will be different magneticpath which is isolated from the path for the fundamental flux component.

The manner in which such intermodulation is prevented by this inventionmay now be better realized upon referring to FIGURE 9 which shows thetreatment of av set of coil sides in a slot.

As shown in FIGURE 9, a bundle of coil sides 60, in the circuit ofprimary winding 26, is disposed in a slot 61 between two teeth 63 and64. A layer or wrapping of paper or fabric 65 is provided to encirclethe coil -sides after all' the coil turns are dropped into the slot 61.

On the outside of the paper or fabric wrapper 65 is a layer or wrapperof magnetizable metal foil '70 to constitute a short confining magneticpath for the harmonic ux components of the flux eld to be induced by thecoil sides when the primary Winding is energized. In an actualgenerator, the slots are tightly packed with coil sides, paper andfoil.The two slots show the general arrangement of paper and foil during andafter application. The foil 70 is softly magnetizable material withminimum retentivi-ty, and is commercially available in thicknesses inthose two regions and different cross-sectional areas of the foil may beappropriate to absorb and become saturated by the harmonic fluxcomponents of the field. The teeth and cores and end laminations arefree of the magnetic turbulence which characterizes the conventionalstructure depicted in FIGURE 3. Although the application of the foil tothe 4primary alone will prevent the transmission of false `signals inthe first instance, similar application of foil to the secondary alsowill serve to prevent regeneration of harmonics by the secondarywindlng.

The core arrangement shown in FIGURES 3 and 3-A, with windings onseparate cores, spaced by the air gap, is one form of tachometergenerator. As initially mentioned, another form, as in FIGURE 10, has asingle core 81 to support both windings 82 and 83 in electricalquadrature space disposition, with an air gap 84 separating the core 81and a flux return element 85 to accommodate a rotor cup S6. The coilarrangement corresponds to the dropping of the secondary Winding coils27 down onto the core 21 of the primary in the corresponding relativepositions shown in FIGURES 3 and 3-A.

As shown in FIGURE 9, the foil 70 is shown in contact with the edges ofthe laminations at the slot. It will be understood, of course, that aninsulating liner may be employed between the foil and the core. By useof the magnetic tape of my co-pending application Serial No. 51,696filed Iune 25, 1963, previously referred to, the insulating liner isplaced in position together with the magnetizable matter functionallycorresponding to the foil, all in one operation, to place themagnetizable material between the insulation wrapping 65 and theinsulation base of the magnetic tape. Thus, in the sl-ot in FIG- URE 9,such magnetic tape would have a layer of insulation between the core 64and the magnetizable material on the tape. Also, at the overlap ofthetape, the insulation base would provide a slight dielectric spacingbetween the magnetizable material at the overfolded parts of themagnetic tape.

A modication of FIGURE the omission ofthe foil 70, leaving the windingconductors 60 wrapped with the insulation 65, and the use of a magneticwedge as disclosed in said-co-pending application Serial No. 51,696,filed June 25, 1963. The magne-tic layer or content of the wedge wouldprovide a magnetic bridging path between the adjacent tooth edges, atthe mouth of the slot, to conduct the harmonic magnetic flux componentsand thereby keep them out of the air gap and thus prevent interlinkagewith the cup.

It is intended herein that reference to foil, as the material toestablish the auxiliary magnetic path for the harmonic flux components,shall also include magnetic material in other forms, such as powders,magnetic printing ink, or magnetic strips or filaments cemented orsecured to or woven into tapes or fabrics.

The invention herein thus provides a simple construc- Ition for andmethod of eliminating the harmful effects of harmonic fluxes in atachometer generator, so the zero error voltage or null may beeliminated. The high cost of testing and compensating tachometergenerators is thus also eliminated, and increased accuracy -is directlyobtained in a production device.

The general arrangement and details of construction of the tachometergenerator, and the construction and disposition of the magnetic materialfor diverting, guiding and confining the harmonic flux components, maybe variously modified within the scope of the invention withoutdeparting from the spirit and scope of the claims.

What is claimed is: Y

1. a tachometer generator to operate around an axis of rotation, andcomprising (a) a cylindrical stator core disposed concentrically aboutthe axis, .and supporting (l) `an input winding to be energized from anexternal source, and

(2) an output winding to be inductively energized from said inputwindin-g;

(b) a cylindrical magnetic iiux return concentrically disposed aroundsaid same axis and spaced radially outward from the' stator core to denea concentric cylindrical gap tbetween the magnetic iiux return and thestator core;

(c) a co-axial drive shaft;

(d) a rotor cup supported on the drive shaft and disposed to extendconcentrically into -said gap, to be rotated by the shaft to transferenergy lfrom the input winding to the outputwinding first by inductivereaction between the magnetic flux field from the input winding and thecup, and then by inductive reaction between the cup and the outputwinding; and

(e) magnetizable means disposed between the input Winding and the airgap, said means being responsive to yhigher harmonic components of theflux field developed by the input winding, and said means serving toconfine said hanmonic flux components over a par-t of their magneticpath to a magnetic path shunting the air gap and thus serving to preventsaid harmonic iiux components .from reaching and influencing the rotorcup, Ithereby to prevent energy from those higher harmonic componentsfrom being transfer-red by the cup and from reaching and affecting theoutput winding. l

2. A tachometer generator comprising 9 could be achieved, withl (a) aprimary Winding to be energized from an external source;

(b) a second winding to be inductively energized from the primarywinding only under certain operating conditions;

(c) means adjacent the windings defini-ng an air gap v through which theinduction magnetic field of the primary winding must pass to beavailable for transferring energy to the secondary winding;

(d) a member of non-magnetic material movable in said air gap andeffective only durin-g its movement to transfer energy inductively fromthe primary winding to the secondary winding; and

(e) magnetizable means disposed between the primary winding and the air.gap and serving to divert undesirable harmonic flux components of themagnetic -ilux field gener-ated by the primary winding when energized,said magnetizable means operating to divert and to conduct and toisolate and to sepa-rate said undesirable harmonic iiux field componentsfrom the desirable iiux field generated by the primary winding and m-adeavailable to lthe movable member for inductive energy transfer, saidmagnetizable means serving to direct said diverted undesirable fluxcomponents into a path to by-pass the air gap and thereby leave only adesirable component to be transferred by the movable member.

3. A t-achometer generator comprising (a) an inner cylindrical coreconcentrically surrounding a main central axis of rotation;

(b) input and output windings of said inner core;

(c) an outer cylindrical co-re surrounding said inner core andconcentric therewith about said axis, and said outer core bein-g spacedfrom the inner core to define a concentric cylindrical air gap, and saidouter core serving to complete the magnetic circuit for said inner core;

(d) a yrotatable cup extending into said air gap and operative, uponrotation, to Itransfer energy by induction from one winding .as theinput winding to the other winding as the output winding by inductivereaction with the magnetic iiux ylield generated by the input windingupon energization from an external alternating current source; and

(e) magnetic flux conducting means disposed between the primary windingand the air gap and serving to divert .undesirable higher harmonictiuxcomponents from the total magnetic Iflux field as generated by the inputwinding, to a confining path including said means that does notinterlink with the cup or with the output winding.

4. A tachometer generator comprising (a) a margnetizable core;

(b) a primary winding thereon to be energized from an externalalternating current source;

(c) a secondary winding also on the core to receive energy from theprimary winding;

(d) a magnetic flux return spaced from the air gap;

(e) a rotor cup rotatable in the gap between the core and the magnetic:ux return to transfer electromagnetic energy from the primary windingto the secondary winding; and

(f) .auxiliary magnetizable means disposed in close proximity to bothwindings and between said windings and the air gap, and serving toselectively isolate undesired harmonic ux components and thereby preventItransfer to the cup and to the secondary winding of any energy from theprimary winding that is contained in said undesired higher harmonics ofthe magnetic flux field generated by the input winding.

5. A tachometer generator, as in claim 4, in which theenergy-transfer-preventing means that isolates the higher harmonicenergy from the total flux iield before the field energy reaches therotor cup, consists of magnetcore by an izable material disposed betweenthe windings and magnetizable core.

6. A tachometer generator comprising (a) a primary winding to beenergized from an external source;

(b) a second winding to be inductively energized from the primaryWinding only under certain operating conditions;

(c) magnetizable core means adjacent the windings and detining -an airgap through which the induction magnetic field ofv the primary windingmust pass to be available yfor transferring energy to the secondarywinding;

(d) a member of non-magnetic material movable in the said air gap andeffective only during its movement to transfer energy inductively fromthe primary winding to the .secondary winding; and

(e) auxiliary magnetizable means disposed between said windings and saidcore means `for preventing magnetic flux interlinkage between the memberof non-magnetic .material and the two windings by the higher harmonicsof the magnetic flux field as generated by the primary winding.

7. A tachometer generator, as in claim 6, in which the auxiliarymagnetizable means (e) consists of a magnetizable flux barrier betweenthe cup and the two windings, the flux barrier having such physical andmagnetic parameters as to .become saturated by the hi-gher harmoniccontent of lthe magnetic -ux field as generated by the primary winding.

8. A tachometer generator, as in claim `6, in which the auxiliarymagnetizable means consists of a thin foil of magnetizable ma-terialencircling the active coil sides of each coil in the slots.

9. A tachometer generator, as in claim 6, in which the auxiliarymagnetizable means consists of a thin foil of magnetizable materialencircling the active coil sides of each coil in the slots, andalso-encircling the end connections between the coil sides.

10. A tachometer generator, as in claim 9, in which the auxiliarymagnetizable material becomes saturated by the harmonic flux componentsand the leakage flux of the end turns.

11. A tachometer generator to opera-te around an axis of rotation, andcomprising (a) a cylindrical stator core disposed concentrically aboutthe axis and supporting (1) an input winding to be energized from anexternal source, and

(2) an output winding to be inductively energized from said inputwinding;

(lb) a cylindrical magnetic flux return concentrically disposed aroundsaid same axis and spaced radially outward from the stator core todefine a concentric cylindrical gap between the (magnetic fiux returnand the stator core; i

(c) a co-axial drive shaft;

(d) a rotor cup supported on the drive shaft and disposed to extendconcentrically into said gap, to be rotated |by the shaft to transferenergy from the input winding to the output winding first by inductiverecation between the magnetic flux field from the input winding and thecup, and then by inductive reaction between the cup and the outputwinding; and

(e) means for confining the energy of the harmonic flux components andof the leakage flux of the flux field developed by the input winding,said confining means constituting a magnetizable `shell disposed be- 12tween the input winding and the stator core, and serving to keep saidharmonic flux components from entering the air -gap and from inuencingthe rotor cup.

12. A tachometer as in claim 11, in which the confining meansconstitutes a close magnetizable shell saturable by the harmonic fluxcomponents of the flux field of the input winding.

13. A tachometer generator comprising (a) a primary winding to beenergized from an external alternating voltage source; 1

(b) a secondary winding disposed in electrical quadrature inductiverelation relative to the primary winding;

(c) a rotor rotatable in a prescribed path to be traversed by themagnetic fiux field generated by the primary winding while it isenergized, said rotor being intended to be the sole medium fortransferring energy inductively from the primary winding to thesecondary and `only while said rotor is rotating;

(d) and magnetizable foil encircling all portions of the primary windingthat are positioned to establish a magnetic flux field across the pathto be traversed by the rotor.

14. A tachometer generator, as in claim 13, in which the magnetizablefoil (d) becomes magnetically saturrated by harmonic magnetic fluxcomponents in the flux field generated by the primary winding.

15. Atachometer generator comprising (a) a primary stator core providedwith a series of slots spaced symmetrically angularly about a centralaxis;

(b) a secondary stator core provided with a series of spaced slots alsosymmetrically anlgularly spaced aroundvsaid axis, and said secondarycore being spaced from the primary stator core by a narrow symmetricalair gap concentric -with said axis;

(c) a multi-coil input winding symmetrically distributed in the slots ofthe primary core, and to be energized from an external alternatingVoltage source;

(d) a multi-coil output winding symmetrically distributed in the slotsof the secondary core and an- `gularly shifted relative to the primarywinding so the two windings are in electrical time quadrature relation;

(e) a co-axial rotatable shaft;

(f) a rotor of non-magnetic material secured to the shaft to be driventhereby and disposed concentrically in the air gap between the two coresto transfer energy from the primary winding into the secondary windingby induction in time quadrature only during rotation of the rotor;

(g) and means consisting of magnetizable foil wrapped around the coilsides of the input winding to serve 4as a restricting path for harmonicelectro-magnetic flux components in the ux field developed by the inputwinding when energized.

16. A tachometer generator as in claim 15, in which the magnetizablefoil becomes saturated by the harmonic flux components.

17. A tachometer generator as in claim 15, in which the foil is wrappedaround the entire coil including coil Asides and end turns, and is oflimited cross-sectional area to be saturable by the harmonic fluxcomponents and leakage flux.

No references cited.

MILTON O. HIRSHFIELD, Primary Examiner.

1. A TACHOMETER GENERATOR TO OPERATE AROUND AN AXIS OF ROTATION ANDCOMPRISING (A) A CYLINDRICAL STATOR CORE DISPOSED CONCENTRICALLY ABOUTTHE AXIS, AND SUPPORTING (1) AN INPUT WINDING TO BE ENERGIZED FROM ANEXTERNAL SOURCE, AND (2) AN OUTPUT WINDING TO BE INDUCTIVELY ENERGIZEDFROM SAID INPUT WINDING; (B) A CYLINDRICAL MAGNETIC FLUZ RETURNCONCENTRICALLY DISPOSED AROUND SAID SAME AXIS AND SPACED RADIALLYOUTWARD FROM THE STATOR CORE TO DEFINE A CONCENTRIC CYLINDRICAL GAPBETWEEN THE MAGNETIC FLUX RETURN AND THE STATOR CORE; (C) A CO-AXIALDRIVE SHAFT; (D) A ROTOR CUP SUPPORTED ON THE DRIVE SHAFT AND DISPOSEDTO EXTEND CONCENTRICALLY INTO SAID GAP, TO BE ROTATED BY THE SHAFT TOTRANSFER ENERGY FROM THE INPUT WINDING TO THE OUTPUT WINDING FIRST BYINDUCTIVE REACTION BETWEEN THE MAGNETIC FLUX FIELD FROM THE INPUTWINDING AND THE CUP, AND THEN BY INDUCTIVE REACTION BETWEEN THE CUP ANDTHE OUTPUT WINDING; AND (E) MAGNTIZABLE MEANS DISPOSED BETWEEN THE INPUTWINDING AND THE AIR GAP, SAID MEANS BEING RESPONSIVE TO HIGHTER HARMONICCOMPONENTS OF THE FLUX FIELD DEVELOPED BY THE INPUT WINDINGS, AND SAIDMEANS SERVING TO CONFINE SAID HARMONIC FLUX COMPONENTS OVER A PART OFTHEIR MAGNETIC PATH TO A MAGNETIC PATH SHUNTING THE AIR GAP AND THUSSERVING TO PREVENT SAID HARMONIC FLUX COMPONENTS FROM REACHING ANDINFLUENCING THE ROTOR CUP, THEREBY TO PREVENT ENERGY FROM THOSE HIGHERHARMONIC COMPONENTS FROM BEING TRANSFERRED BY THE CUP AND FROM REACHINGAND AFFECTING THE OUTPUT WINDING.